1. Field of the Invention
The invention relates to superhard polycrystalline material elements for earth drilling, cutting, and other applications where engineered superhard surfaces are needed. The invention particularly relates to polycrystalline diamond and polycrystalline diamond-like (collectively called PCD) elements with dual edged working surfaces.
2. Description of the Related Art
Polycrystalline diamond and polycrystalline diamond-like elements are known, for the purposes of this specification, as PCD elements. PCD elements are formed from carbon based materials with exceptionally short inter-atomic distances between neighboring atoms. One type of diamond-like material similar to PCD is known as carbonitride (CN) described in U.S. Pat. No. 5,776,615. In general, PCD elements are formed from a mix of materials processed under high-temperature and high-pressure into a polycrystalline matrix of inter-bonded superhard carbon based crystals. A common trait of PCD elements is the use of catalyzing materials during their formation, the residue from which, often imposes a limit upon the maximum useful operating temperature of the element while in service.
A well known, manufactured form of PCD element is a two-layer or multi-layer PCD element where a facing table of polycrystalline diamond is integrally bonded to a substrate of less hard material, such as tungsten carbide. The PCD element may be in the form of a circular or part-circular tablet, or may be formed into other shapes, suitable for applications such as hollow dies, heat sinks, friction bearings, valve surfaces, indentors, tool mandrels, etc. PCD elements of this type may be used in almost any application where a hard wear and erosion resistant material is required. The substrate of the PCD element may be brazed to a carrier, often also of cemented tungsten carbide. This is a common configuration for PCD's used as cutting elements, for example in fixed cutter or rolling cutter earth boring bits when received in a socket of the drill bit, or when fixed to a post in a machine tool for machining.
PCD elements are most often formed by sintering diamond powder with a suitable binder-catalyzing material in a high-pressure, high-temperature press. One particular method of forming this polycrystalline diamond is disclosed in U.S. Pat. No. 3,141,746 herein incorporated by reference for all it discloses. In one common process for manufacturing PCD elements, diamond powder is applied to the surface of a preformed tungsten carbide substrate incorporating cobalt. The assembly is then subjected to very high temperature and pressure in a press. During this process, cobalt migrates from the substrate into the diamond layer and acts as a binder-catalyzing material, causing the diamond particles to bond to one another with diamond-to-diamond bonding, and also causing the diamond layer to bond to the substrate.
The completed PCD element has at least one body with a matrix of diamond crystals bonded to each other with many interstices containing a binder-catalyzing material as described above. The diamond crystals comprise a first continuous matrix of diamond, and the interstices form a second continuous matrix of interstices containing the binder-catalyzing material. In addition, there are necessarily a relatively few areas where the diamond-to-diamond growth has encapsulated some of the binder-catalyzing material. These ‘islands’ are not part of the continuous interstitial matrix of binder-catalyzing material.
In one common form, the diamond body constitutes 85% to 95% by volume and the binder-catalyzing material the other 5% to 15%. Such an element may be subject to thermal degradation due to differential thermal expansion between the interstitial cobalt binder-catalyzing material and diamond matrix beginning at temperatures of about 400 degrees C. Upon sufficient expansion the diamond-to-diamond bonding may be ruptured and cracks and chips may occur.
A common problem with these PCD elements, especially when used in highly abrasive cutting application, such as in drill bits, has been the limitation imposed between wear resistance and impact strength. This relationship has been attributed to the fact that the catalyzing material remaining in the interstitial regions among the bonded diamond crystals contributes to the degradation of the diamond layer.
It has become well known in the art to preferentially remove this catalyzing material from a portion of the working surface in order to form a surface with much higher abrasion resistance without substantially reducing its impact strength. This new type of PCD element is described in U.S. Pat. Nos. 6,601,662; 6,592,985 and 6,544,308 all these U.S. patents incorporated by reference herein for all they disclose.
PCD elements made in accordance with these and in other related patents have become widely used in the oilfield drilling industry. One surprising observation resulting from this usage, however, has been an increase in the cutting efficiency of these cutters, which has been manifested in higher drilling rates of penetration—typically by 40%, but occasionally by as much as a factor of two to four times.
In observing these PCD cutting elements in the worn condition, it was discovered that the differential wear rate caused a protruding lip to form on the wear edge of the working surface. This lip caused the PDC cutting element to appear ‘sharper’ to the earth formation being drilled, producing the higher drilling rates of penetration.
U.S. Pat. No. 4,976,324 describes an arrangement in which a vapour deposition technique is used to apply a catalyst free diamond layer to a surface of a cutting element, but it will be appreciated that the vapour deposition technique used does not bond the diamond layer to the underlying diamond table. U.S. Pat. No. 6,068,913 and U.S. Pat. No. 4,766,040 both describe multi-layered elements, and U.S. Pat. No. 6,187,068 describes providing the element with concentric ring shaped regions of different abrasion resistance.
An arrangement is described in U.S. Pat. No. 6,189,634 in which, when worn, part of the substrate of a cutting element becomes exposed at the working surface.